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1997, pp 91 94.143.L Levine, BA Drew.Rheological and engineering aspects of the sheeting and lami-nating of dough.In: H Faridi, JM Faubion, eds.Dough Rheology and Baked Prod-uct Texture.New York: Van Nostrand, 1990, pp 513 557.144.L Levine, E Boehmer.The fluid mechanics of cookie dough extruders.J Food ProcEng 15:169 186, 1992.Copyright 2003 by Marcel Dekker, Inc.All Rights Reserved.8Stress and Breakage in FormedCereal Products Induced by Drying,Tempering, and CoolingBetsy WillisSouthern Methodist University, Dallas, Texas, U.S.A.Martin OkosPurdue University, West Lafayette, Indiana, U.S.A.I.INTRODUCTIONThe quality of value-added cereal products is judged by many criteria, includingflavor, aroma, color, texture, and overall appearance.These quality attributes aredirectly influenced by raw materials and processing conditions.One of the mostchallenging quality characteristics to address is breakage.Drying, tempering, andcooling affect the moisture and temperature gradients in a product and thus havethe potential to cause breakage.Optimal drying, tempering, and cooling conditions depend on the materialbehavior as reflected in its material properties.Temperature gradients in cerealproducts equilibrate rapidly, so the main cause of stress development and break-age is moisture gradients.Process conditions are optimized to maximize productquality and minimize moisture gradients.For example, pasta s dense structure isachieved by shrinkage during moisture removal under high temperature and rela-tive humidity conditions.Optimization of the drying conditions requires knowl-edge of the effects of variations in raw materials and processing (e.g., mixing,extrusion, sheeting) on raw product structure.The behavior of the raw productis reflected in the material properties, which influence mass transfer and stressdevelopment and necessary change with temperature and moisture.To preventbreakage, a product should be dried, tempered, and cooled under conditions thatminimize moisture gradients.Copyright 2003 by Marcel Dekker, Inc.All Rights Reserved.Drying, tempering, and cooling conditions are optimized either by planttests or by numerically simulating the process using mechanistic models.Planttests are lengthy and costly due to the time required to see the result of a processchange and due to the loss of salable product produced during the tests
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